Osteosynthetic Implant With An Embedded Hinge Joint

ABSTRACT

An osteosynthesis implant includes at least one coupling in the form of a swivel joint. Each swivel joint includes at least one planar or annular swivel element and two connecting arms that define a pivot axis. The coupling permits rotation about each pivot axis. The implant and coupling may be formed of unitary construction, or a separate coupling may be connectable to the implant. The coupling may receive a bone fastener such as a bone screw, or may be used in applications that require the coupling to directly support portions of the body such as spinal features.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior patent application Ser. No.09/714,147, filed Nov. 17, 2000, which in turn is a continuation of theU.S. National Stage designation of co-pending International PatentApplication PCT/CH98/00208, filed May 19, 1998, the entire contents ofwhich are expressly incorporated herein by reference thereto.

FIELD OF THE INVENTION

The invention relates to an implant with a coupling. More particularly,the invention relates to osteosynthesis implants with couplings havinggimbal-type swivel joints.

BACKGROUND OF THE INVENTION

Angularly fixed longitudinal supports such as plates and barsincreasingly are used in osteosynthesis applications. Such devices areparticularly useful for treating fractures that are located near joints,or for anchoring screws in the spinal column. In applications that useshort screws, the screws typically can be inserted in the longitudinalsupport at a preset angle without presenting problems. When longerscrews are necessary, a fixed, system-dependent orientation of the screwmay be impractical or unwieldy.

To facilitate the use of longer screws in regions such as the spine,special ball joints have been developed. In addition, as disclosed inGerman patent DE 195 48 395, bone plates have been proposed withspecially configured screw holes drilled therein for acceptingcorrespondingly shaped screw heads. The bone screw thus may be locked inplace in the bone plate in a relatively randomly selectable orientation.But, the complexity, bulky nature, and insufficient strength provided bythe connections of these ball joints and screw head-boreholeconfigurations does not sufficiently remedy the inherent problemsencountered with fixed, system-dependent orientations of screws.

Also disclosed in German patent DE 24 38 669 to Bezold is anosteosynthesis bone plate with screw holes having a respective spacingthat can be manipulated using externally generated forces. The screwholes are arranged in the form of lugs punched out of the main body ofthe osteosynthesis plate and connected thereto merely by elastic legs.In one embodiment, the legs are aligned along one axis and connected tothe lug diametrically relative to the axis. When the lug is lifted outof the plane of the plate, the legs are bent such that the rotationalaxis of the lug no longer coincides with the vertical axis of either thelug itself or the screw hole. Use in clinical applications thus islimited because as the lug is turned, the center of the screw hole isundesirably shifted.

There exists a need for a bone plate with a coupling that facilitatesthe use of a wide range of sizes of bone screws. There further exists aneed for a coupling that requires less space than ball joints andprovides simplicity in design and use. Additionally, there is a need fora substantially flat swivel joint for use in connecting implantcomponents such as a bone screw and a bone plate.

The present invention provides an implant and coupling capable offurnishing these improvements, and advantageously has application in awide range of other implants unrelated to bone screw support.

SUMMARY OF THE INVENTION

The present invention relates to an osteosynthesis implant that includesa coupling comprising at least one annular element having a pair ofconnecting members for coupling the annular element to a surroundingstructure. The connecting members provide the annular element with aswiveling motion with respect to the surrounding structure for alignmentof the annular element during insertion or implantation of the implant.The connecting members also form a single coupling axis with thesurrounding structure and the annular element swivels about thatcoupling axis.

In one embodiment, the annular element defines a hole for receiving afastener and the surrounding structure is the implant. Typically, theannular element has a generally circular configuration and defines agenerally cylindrical hole that extends along a central axis. Also, thehole is generally perpendicular to at least one of the top and bottomsurfaces of the annular element.

In another embodiment, the annular element has a top surface, a bottomsurface, and a first thickness defined between the top and bottomsurfaces, and the implant has a top implant surface, a bottom implantsurface, and a second thickness defined between the top and bottomimplant surfaces and the connecting members have a connection thickness.Typically, the first thickness of the annular element is less than orequal to the second thickness of the implant and the connectionthickness of the connecting members is also less than or equal to thesecond thickness of the implant.

In another embodiment, the coupling has inner and outer annular elementswhere each element has a pair of connecting members and the connectingmembers of the inner annular element are coupled to the outer annularelement and the connecting members of the outer annular element arecoupled to a surrounding structure. This permits the inner annularelement to be provided with a first swiveling motion and the outerannular element to be provided with a second swiveling motion. Also, theconnecting members of the inner annular element form a first couplingaxis and the connecting members of the outer annular element form asecond coupling axis that is positioned at an angle with respect to thefirst coupling axis. The first and second coupling axes can besubstantially perpendicular to each other.

In another embodiment of the present invention, the inner and outerannular elements, the connecting members and the implant are all formedof unitary construction and each connecting member is capable ofexhibiting elastic deformation to permit the annular element to swivel.

In another embodiment, the implant is an intervertebral element havingat least one surface that includes the surrounding structure in whichthe inner and outer annular elements are disposed so that more precisealignment can be provided. In an exemplary embodiment, theintervertebral element has two parallel surfaces, each of which providesthe surrounding structure in which the inner and outer annular elementsare disposed. The two parallel surfaces define a central longitudinalaxis and the intervertebral element has a first through-hole extendinggenerally perpendicular to the central longitudinal axis and has asecond through-hole extending generally perpendicular to the firstthrough-hole.

In another exemplary embodiment. the intervertebral element has top andbottom surfaces, each of which provide the surrounding structure inwhich inner and outer annular elements are disposed, In addition, thetop and bottom surfaces are, typically, configured as generally ovalplates and are spaced apart from each other with a central connectorthat is generally cylindrical, Furthermore, the central connector isfixed to the inner annular elements, such that swivelling of the platesis permitted while the inner annular elements remain parallel to eachother and the connecting members of the inner annular element form afirst coupling axis and the connecting members of the outer annularelement form a second coupling axis that is generally perpendicular tothe first coupling axis. Typically, the implant is configured anddimensioned to be received between two vertebral bodies.

In another embodiment of the present invention, the surroundingstructure in which inner and outer annular elements are disposed is afixation system for a longitudinal support. The fixation systemcomprises a mounting head having a top surface and bottom surface, afirst head bore which extends from the top head surface to the bottomhead surface about a head bore longitudinal axis and a second head borewhich extends substantially perpendicular to the first head bore. Thesecond head bore is configured and dimensioned to receive a longitudinalsupport and the inner annular element includes a hole for a pediclescrew.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIG. 1A shows a cross-sectional view of an implant of the presentinvention in which a swivel joint is integrated in a bone plate;

FIG. 1B shows a top view of the implant of FIG. 1A;

FIG. 2 shows a top view of another implant of the present invention inwhich a double-gimbaled swivel joint is integrated in a bone plate;

FIG. 3 shows a partial, cross-sectional view of yet another implant ofthe present invention in which swivel joints are integrated in two femurplates and receive a hip screw;

FIG. 4A shows a partial cross-sectional view of an additional implant ofthe present invention in which a swivel joint is integrated in avertebral fixation element;

FIG. 4B shows a side view of the implant of FIG. 4A;

FIG. 4C shows a top view of a swivel joint used in the implant of FIG.4A;

FIG. 5 shows a perspective view of another implant of the presentinvention in which a swivel joint is integrated in a vertebral unit;

FIG. 6 shows a cross-sectional view of yet another implant of thepresent invention in which a vertebral unit is integrated with a swiveljoint;

FIG. 7 shows a side view of the implant of FIG. 6; and

FIG. 8 shows another side view of the implant of FIG. 6 with thevertebral end plates disposed at an angle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to an osteosynthetic implant or implantcomponent having at least one swivel joint connected thereto andpreferably being in the form of a planar gimbal articulation. The atleast one swivel joint preferably includes a planar, disc-shaped orannular swivel element having two flat, bar-shaped connecting elementspositioned along a common axis at the outer perimeter of the swivelelement. The connecting elements or legs define axes of rotation. Eachswivel joint includes at least one swivel element that is rotatablyconnected to the implant or implant component via the connectingelements. The inner swivel element may be provided with a boreholegenerally perpendicular to the plane of rotation defined by the axes ofrotation of the swivel element. The implant or implant component and theswivel joints may be an integral unit, or connecting legs in the form ofpivot shafts may be positioned between the planar or annular swiveljoint and the implant in such a fashion that the swivel joint isconcentrically supported in a borehole of an osteosynthesis implantcomponent and is rotatable around the pivot axes.

The connecting elements may be dimensioned so that elastic deformationthereof permits an angularly fixed rotation of the swivel elementrelative to the implant or implant component. The connecting legs aresituated opposite each other along one axis, with their outer lateralsurfaces attached to the implant or implant component while their innerfaces are attached to a planar or annular swivel joint.

In one preferred embodiment, the swivel joint includes two nested,coplanar swivel elements, with each inner swivel element being connectedvia two connecting elements to a corresponding outer swivel element topermit rotation around a first axis. Likewise, the outer swivel elementis connected via two connecting elements to the implant or implantcomponent to permit rotation around a second axis. The axis of rotationmay extend between the nested swivel elements along the plane in whichthe swivel elements are situated, and the axes of rotation may be offsetby 90.degree. from each other. The swivel joint may be configured as aplanar, double-gimbal swivel joint. Thus, the two swivel elements aregimbal-mounted within a single implant component borehole, with an outerswivel element being rotatably supported in the borehole of theosteosynthesis implant component and the inner swivel element beingrotatably supported in the borehole of the outer swivel element.

The connecting elements may be shafts that are pivot-mounted in at leastone swivel element and in the implant or implant component. In addition,the swivel elements and the implants or implant components may beseparated by slots extending to the connecting elements. which may be inthe form of generally arcuate or circular segments.

The implant incorporating the swivel joint may be a block-shaped boneplate, and the thickness of the swivel element and connecting elementsmay be less than the thickness of the bone plate, other implant, or thewall of an osteosynthesis implant component accommodating the swiveljoint. The swivel joint is integrated with the bone plate.

In another preferred embodiment, the swivel joint is integrated in amounting head for connecting a pedicle screw to a longitudinal supportwithin a spinal vertebra fixation system. The swivel joint includes atleast one swivel element, with the mounting head serving to connect thelongitudinal support to the pedicle screw. The swivel joint and mountinghead may be an integral unit. The implant may be configured as anintervertebral unit or as a vertebra substitute. Such an intervertebralunit may have a swivel joint integral with its top and bottom surfacesfor adapting to adjacent vertebra.

In a further preferred embodiment, two swivel joints are attached bytheir inner swivel elements to the ends of a rod in a directiongenerally perpendicular to their axes of rotation, with one swivelelement of each swivel joint being connected to a vertebral end plate.The vertebral end plates contacting the vertebrae are in the form ofoval rings which are connected to outer swivel elements and each outerswivel element, in turn, is connected to each respective inner swivelelement. Each of the two vertebral end plates is connected to the rod byway of a swivel joint, each rotatable around at least one axis ofrotation.

The swivel joint may be configured for holding a bone fastener. A bonescrew or pedicle screw may extend through a borehole in the swivelelement, with the screw head bearing against the swivel element, so thatthe swivel joint permits the screw head to rotate within the bone plateor vertebral fixation system about at least one axis. The borehole inthe swivel element may be tapered and a bone fastener such as a bonescrew or pedicle screw may have a correspondingly conical screw head soas to permit an angularly fixed connection between the implant orimplant component and the bone fastener. Furthermore, the borehole inthe swivel element may be provided with internal threading to be engagedby external threading on the screw head or shank of the bone screw orpedicle screw, thus permitting an angularly fixed connection between theimplant or implant component and the bone fastener. The threading may betapered.

The bone screw or the pedicle screw may be provided with an expandablehead, and by means of a clamping screw, the parts of the expandablescrew head are pressed with a positive fit against the wall of theborehole so as to permit an angularly fixed connection between theimplant or implant component and the bone fastener.

Referring to FIGS. 1A and 1B, bone fixation system 100 includes boneplate 3 with couplings 10 in the form of swivel joints 49 mountedtherein. In a preferred embodiment, bone plate 3 is provided with atleast one screw hole 7 that extends from top surface 13 to bottomsurface 14 of bone plate 3 about a center axis 12 and serves toaccommodate a fastener 1 such as a bone screw. Screw hole 7 has an innerwall 7′. Swivel joint 49 including a circular inner swivel element 4 andtwo coaxial inner connecting legs 5. Inner connecting legs 5 connectinner swivel element 4 to bone plate 3. Preferably, inner swivel element4 has an annular shape, with a central borehole 8′ and an outerperimeter 9′. When circular inner swivel element 4 with inner connectinglegs 5 is disposed in screw hole 7, two near semicircular slots 6 aredefined between wall 7′ of bone plate 3 and perimeter 9′ of inner swivelelement 4, the slots 6 being concentric with screw hole 7. Preferably,slots 6 are milled into bone plate 3, although slots 6 may be formedotherwise. Inner connecting legs 5 and inner swivel element 4 may beunitarily constructed from the same blank and are integral parts of boneplate 3.

Inner swivel element 4 of swivel joint 49 has a thickness T.sub.adefined vertically between upper swivel element surface 70 and lowerswiveling element surface 72, and bone plate 3 has a thickness T.sub.bdefined vertically between top surface 13 to bottom surface 14.Preferably, legs 5 have a thickness that is substantially the same asthickness T.sub.a. In the preferred embodiment, thickness T.sub.a ofcoupling 10 is less than the thickness T.sub.b of plate 3.

As shown in FIGS. 1A and 1B, coupling 10 with inner connecting legs 5 isin the form of a single gimbal or universal joint. Coaxial connectinglegs 5 of swivel joint 49 define an axis of rotation 11 that is disposedtransverse to the longitudinal direction of bone plate 3. When a bonescrew 1 is inserted into central borehole 8′ of inner swivel element 4and screw head 2 of bone screw 1 bears against upper swivel elementsurface 70, swivel joint 49 permits rotation of inner swivel element 4about axis of rotation 11. Thus, bone screw 1 may be oriented at adesired angle and screwed into a bone.

Turning now to FIG. 2, another preferred embodiment of coupling 10 foruse with a bone fixation system 100 is shown. Swivel joint 50 isprovided with a circular outer swivel element 16 having outer connectinglegs 15. A circular inner swivel element 4 is coupled to circular outerswivel element 16 with inner connecting legs 5, while circular outerswivel element 16 is coupled to bone plate 3 with outer connecting legs15. Two near semicircular slots 74 are defined between perimeter 9′ ofinner swivel element 4 and first perimeter 76 of outer swivel element16. Likewise, two near semicircular slots 17 are defined between secondperimeter 78 of outer swivel element 16 and wall 7′ of bone plate 3.Outer connecting legs 15 are disposed coaxially about an axis 18,permitting outer swivel element 16 to rotate about axis 18.

In the embodiment of FIG. 2, axis 18 is disposed generally parallel tothe longitudinal direction of bone plate 3, while axis 11 is disposedgenerally transverse thereto. Thus, swivel joint 50 permits swivellingabout two non-parallel axes 11, 18. Preferably, axes 11, 18 are offsetby about 90.degree. with respect to each other, permittingdouble-gimbaled action. Inner swivel element 4, inner connecting legs 5,outer connecting legs 15 and outer swivel element 16 may be unitarilyconstructed as integral parts of bone plate 3. Alternatively, innerconnecting legs 5 and outer connecting legs 15 may be pins or othersuitable coupling elements. If pins are used, the pins formingconnecting legs 15 are supported in bone plate 3 and inner swivelelement 4, while the pins forming legs 5 are supported in outer swivelelement 16 and inner swivel element 4.

Referring to FIG. 3, a bone fixation system 200 includes a bone fastenerin the form of a hip screw 19 along with upper and lower bone plates 3,26, each having a coupling 10. Hip screw 19 may enter bone plate 3 at anoblique angle, and thus may be supported in bone plate 3 by means of acoupling 10 such that screw head 20 of hip screw 19 bears against innerswivel element 4 of coupling 10. Preferably, since hip screw 19 does notextend perpendicular to bone plate 3, inner swivel element 4 is tiltedin the desired direction prior to implantation of hip screw 19. However,angulation in vivo by a surgeon also may be achieved. A coupling 10suitable for use in bone fixation system 200, for example, may be in theform of either swivel joint 49 or 50, although embodiments of coupling10 with more than two swivel elements forming a swivel joint may also beused. Accordingly, depending on the type of joint used, coupling 10 mayinclude inner connecting legs 5 for a single gimbal joint, or coupling10 may incorporate inner connecting legs 5 and outer connecting legs 15for a double gimbal joint.

Since inner connecting legs 5 and outer connecting legs 15 preferablyprovide fixed connections between bone plate 3 and inner swivel element4, or between bone plate 3, inner swivel element 4 and outer swivelelement 16, orientation of a coupling 10 in bone plate 3 may generate aretractive force. It is desirabie to minimize or eliminate suchretractive forces, as by effectively neutralizing the retractive forcesthrough the use of an additional coupling 10 in a bone plate 26. Inparticular, upper and lower bone plates 3, 26 are placed one on top ofthe other, and shank 21 of hip screw 19 is inserted through theintegrated coupling 10 of each plate. Additional tightening bone screws24 may be used for fastening the two bone plates 3, 26 to bone 25.

By moving bone plates 3, 26 relative to each other, it is possible toadjust and fix the orientation of hip screw 19 in a wide range ofangles. Tightening bone screws 24 may be used to fix bone plates 3, 26in place, and additionally serve to fix the orientation of hip screw 19.Shank 21 of hip screw 19 is inserted in central boreholes 22, 23 ofinner swivel elements 4 of couplings 10 which are provided in boneplates 26, 3, respectively. Due to the use of two couplings 10, whenbone plates 3, 26 are fastened, forces transverse to longitudinal axis27 of hip screw 19 are avoided, notwithstanding the retractive force ofinner connecting legs 5 and outer connecting legs 15.

FIGS, 4A, 4B and 4C show another preferred embodiment of the presentinvention in the form of a vertebral fixation system 300. Coupling 10 isused to connect pedicle screw 29 to mounting device 34, which has afirst end 80 and a second end 82. Preferably, first end 80 of mountingdevice 34 is configured for threadable engagement with a fastening nut33, so that the location of mounting device 34, and consequently theposition of pedicle screw 29, may be fixed on a longitudinal support 32that extends through a borehole 86. A coupling 10 is disposed in secondend 82 of mounting device 34, and preferably coupling 10 includes aninner swivel element 4, an outer swivel element 16, inner connectinglegs 5, and outer connecting legs 15, as previously described herein.Inner swivel element 4, outer swivel element 16, inner connecting legs 5as well as outer connecting legs 15 are all integrated with mountinghead 31.

A central longitudinal axis 35 extends between first end 80 and secondend 82 of mounting device 34, preferably about the center of a cavity 84in mounting device 34. Pedicle screw 29 is inserted through borehole 28,defined by inner swivel element 4, until screw head 30 makes fullcontact with borehole 28. If pedicle screw 29 does not extend parallelto longitudinal axis 35 of mounting head 31, coupling 10 compensates forthe change in angle. The choice of design for coupling 10 dictates thepermissible angulation of pedicle screw 29. For example, when a swiveljoint 50 having a dual-gimbal swivel joint is employed, it is possibleto rotate the pedicle screw 29 relative to mounting head 31 about twoaxes 36, 37. Alternatively, if a coupling 49 with a single gimbal swiveljoint is used, the coupling only facilitates the rotation of pediclescrew 29 about one axis relative to mounting head 31.

Referring to FIG. 5, another preferred embodiment of the presentinvention is shown in the form of a spinal block, which may serve as anintervertebral element or as a vertebra substitute. Vertebral fixationsystem 400 includes a spinal unit 38 with a pair of opposing couplings10 disposed in the top surface 39 and bottom surface 40. Couplings 10include inner swivel elements 4, which serve as the support surfaces forvertebral sections adjacent to spinal unit 38 upon implantation. Innerswivel elements 4 may be plate-like or annular, and thus may not includea central hole therein. Spinal unit 38 preferably has the general formof a block, further including a front surface 4 i, rear surface 42, andtwo side surfaces 43 and 44. A first through-hole 45 extends from frontsurface 41 to rear surface 42, and a second through-hole 46 extendsbetween side surfaces 43 and 44.

Preferably, top surface 39 and bottom surface 40 of spinal unit 38 arecambered so that the inner swivel elements 4 of the pair of couplings 10form the highest point of top surface 39 and the lowest point of bottomsurface 40. Advantageously, couplings 10 permit spinal unit 38 to beused even when the lower and upper support surfaces in the spinal column(i.e., adjacent vertebral bodies) are not parallel to one another.Couplings 10 may be integrated into top surface 39 and bottom surface 40of spinal unit 38, so that spinal unit 38 and couplings 10 are made ofunitary construction. With reference to FIG. 2, for example, eachcoupling 10 may include an inner swivel element 4 having two opposing,coaxial, inner connecting legs 5 that permit rotation with respect toouter swivel elements 16. Outer swivel elements 16 are connected tospinal unit 38 with two opposing, coaxial, outer connecting legs 15 thatpermit rotation with respect to spinal unit 38. Preferably, outerconnecting legs 15 are offset by about 90.degree. with respect to innerconnecting legs 5. Thus, each inner swivel element 4 serves as a supportsurface for the parts of the spinal column that are adjacent to and incontact with spinal unit 38. Furthermore, each inner swivel element 4preferably permits rotation about two approximately perpendicular axesdisposed proximate top surface 39 and proximate bottom surface 40 ofspinal unit 38.

As shown in FIGS. 6-8 another preferred embodiment of the presentinvention may serve as a spinal implant. Vertebral fixation system 500includes a pair of vertebral end plates 61 that each have a centrallylocated coupling 10. Each coupling 10 includes two nested swivelelements 4, 16 connected to each other via connecting legs 5, 15, sothat rotation of vertebral end plates 61 is permitted. In thepre-rotation base position, swivel elements 4, 16 are disposed about acommon plane formed by axes of rotation 11, 18, which extend parallel tothe support surfaces of vertebral end plates 61. Outer annular swivelelements 16 are connected to vertebral end plates 61 with a pair ofcoaxial connecting legs 15 that generally define axis 11, such thatrotation is permitted about axis In addition, outer annular swivelelements 16 are connected to inner swivel elements 4 with generallycoaxial connecting legs 5, such that rotation is permitted about axis18. Preferably, vertebral end plates 61 are in the form of oval ringsthat define hollow areas 62 between the inner walls 88 of vertebral endplates 61 and the perimeter 90 of outer swivel elements 16.

Moreover, each of the inner swivel elements 4 is attached to one of ends63, 64 of a central body 60, which may be cylindrical and preferably isa rod. Rod 60 is disposed along central axis 87 which also is generallyperpendicular to the plane formed by axes of rotation 11, 18, and thusperpendicular to the pair of opposing, inner swivel elements 4. Each ofthe two vertebral end plates 61 is connected to rod 60 via a coupling 10such that rotation is permitted about two axes 11, 18. Referring inparticular to FIGS. 7-8, vertebral end plates 61 are show in an initialstate in FIG. 7 with a uniform spacing T.sub.c therebetween. Theprovision of a coupling 10 in each of upper and lower vertebral endplates 61, and the provision of a connection between each coupling 10 ofthe two plates, permits vertebral fixation system 500 to angulate basedon forces applied to plates 61. For example, as shown in FIG. 8, thegenerally uniform separation distance T.sub.c may be decreased by anamount .delta . . . sub.1 in one region, while the separation distanceT.sub.c may be increased by an amount .delta . . . sub.2 in anotherregion of system 500.

While various descriptions of the present invention are described above,it should be understood that the various features can be used singly orin any combination thereof. Therefore, this invention is not to belimited to only the specifically preferred embodiments depicted herein.

Further, it should be understood that variations and modificationswithin the spirit and scope of the invention may occur to those skilledin the art to which the invention pertains. For example, in an alternateembodiment, more than two annular swivel elements may be provided. Inaddition, the connecting legs that couple the swivel elements to eachother and also to an implant may not be disposed generally perpendicularwith respect to each other. Still further, the swivel elements may bedetachably connectable to a bone plate, so that a surgeon can choose acoupling with a suitable central bore hole size for receiving a bonescrew having a surgeon-selected diameter or configuration. In yetanother alternate embodiment, fastening elements such as bone screws maybe threadably engaged with one or more couplings. Accordingly, allexpedient modifications readily attainable by one versed in the art fromthe disclosure set forth herein that are within the scope and spirit ofthe present invention are to be included as further embodiments of thepresent invention. The scope of the present invention is accordinglydefined as set forth in the appended claims.

1. (canceled)
 2. A bone fixation system, comprising: a first coupler forcoupling a bone screw to a longitudinal support; a first screw guidingmember including a first screw receiving hole defining a first screwaxis, the first screw receiving hole being sized so that the first bonescrew may be inserted therein only along the first screw axis; first andsecond pivot arms extending radially outward from the first screwguiding member along a first pivot axis to connect the first screwguiding member to the first coupler so that the first screw guidingmember can pivot relative to the first coupler about the first pivotaxis to pivot the first screw axis relative to the first coupler; asecond coupler for coupling a second bone screw to the longitudinalsupport; a second screw guiding member including a second screwreceiving hole defining a second screw axis, the second screw receivinghole being sized so that the second bone screw may be inserted thereinonly along the second screw axis; and third and fourth pivot armsextending radially outward from the second screw guiding member along asecond pivot axis to connect the second screw guiding member to thesecond coupler so that the second screw guiding member can pivotrelative to the second coupler about the second pivot axis to pivot thesecond screw axis relative to the second coupler.
 3. The system of claim2, wherein the longitudinal support is a rod, a longitudinal axis of therod extending substantially perpendicularly to the first and secondscrew axes.
 4. The system of claim 2, wherein the first coupler includesa first channel sized and shaped to receive the longitudinal supporttherein.
 5. The system of claim 4, further comprising a fastener inthreaded engagement with the first coupler to lock the longitudinalsupport within the first channel.
 6. The system of claim 2, wherein thefirst and second bone screws are pedicle screws and wherein thelongitudinal support is a spinal support rod.
 7. The system of claim 2,wherein the first screw receiving hole and a head of the first bonescrew are structured to create an angularly stable connection betweenthe first bone screw and the first screw guiding member to lock thefirst bone screw at the first screw axis.
 8. The system of claim 2,wherein first screw guiding member includes an outer ring coupled to thefirst and second pivot arms and an inner ring coupled to the outer ringby fourth and fifth pivot arms extending along a third pivot axis sothat the inner ring can pivot about the third pivot axis relative to theouter ring.
 9. The system of claim 8, wherein the third pivot axis issubstantially perpendicular to the first pivot axis.
 10. A method fortreating bone comprising the steps of: inserting to a first targetlocation within a living body a first coupler and a first screw guidingmember including a first screw receiving hole defining a first screwaxis, wherein first and second pivot arms extend radially outward fromthe first screw guiding member along a first pivot axis to connect thefirst screw guiding member to the first coupler so that the first screwguiding member can pivot relative to the first coupler about the firstpivot axis; inserting a first bone screw through the first screwreceiving hole along the first screw axis; locking the first bone screwto the first screw guiding member to create an angularly stableconnection therebetween; pivoting the first screw guiding member to adesired angle relative to the first coupler and inserting the first bonescrew into a first target portion of bone along a desired axis; couplingthe first coupler to a longitudinal support; inserting to a secondtarget location within the living body a second coupler and a secondscrew guiding member including a second screw receiving hole defining asecond screw axis, wherein third and fourth pivot arms extend radiallyoutward from the second screw guiding member along a second pivot axisto connect the second screw guiding member to the second coupler so thatthe second screw guiding member can pivot relative to the second couplerabout the second pivot axis; inserting a second bone screw through thesecond screw receiving hole along the second screw axis; locking thesecond bone screw to the second screw guiding member to create anangularly stable connection therebetween; pivoting the second screwguiding member to a desired angle relative to the second coupler andinserting the second bone screw into a second target portion of bonealong a desired axis; and coupling the second coupler to thelongitudinal support.
 11. The method of claim 10, wherein the step ofcoupling the first coupler to the longitudinal support comprisesinserting the rod into a channel of the first coupler and tightening athreaded nut over the channel.
 12. The method of claim 11, wherein thefirst and second bone screws are pedicle screws and wherein thelongitudinal support is a spinal support rod.
 13. The method of claim10, further comprising: locking a head of the first bone screw in thescrew guiding member to create an angularly stable connection betweenthe first bone screw and the first screw guiding member with the firstbone screw locked at the first screw axis.
 14. The method of claim 10,wherein first screw guiding member includes an outer ring coupled to thefirst and second pivot arms and an inner ring coupled to the outer ringby fourth and fifth pivot arms extending along a third pivot axis, themethod further comprising pivoting the inner ring can pivot about thethird pivot axis relative to the outer ring.